The present device relates to microelectromechanical systems. More particularly, the device relates to thermally activated microactuators.
Many different transducers have been created to convert electricity and thermal energy into mechanical force or motion. For example, electric linear and rotary motors, relays, and the like are used for many applications. Relays, in particular, are used to carry out functions such as valving and switching when actuated by a current.
However, previously known transducers are typically ill-suited for use in microcircuits. Microcircuits are used in many different applications, from hearing aids to dog tags, many of which require small-scale mechanical operations. MEMS, or microelectromechanical systems, have been developed to provide mechanical operations in microscopic environments.
Nevertheless, known small-scale transducers, or microactuators, are in may respects limited. They are somewhat bulky with respect to the circuits in which they operate. They also require considerable voltage to operate, and provide only a relatively small amount of mechanical force or displacement in return. The high voltage requirements of most known transducers make them unusable in CMOS circuits, as found in personal computers, which typically operate at 5 Volts or less. In addition, known microactuators are often subject to failure due to contamination, which makes them useless in many exposed environments. Additionally, many known microactuators are inflexible in design, and thus cannot be readily adapted to suit different applications. Known devices also must often be manufactured through special processes that require entirely different equipment and procedures from those used to form a circuit.
One example of a known microactuator is a xe2x80x9cUxe2x80x9d shaped actuator, with a xe2x80x9chotxe2x80x9d arm and a xe2x80x9ccoldxe2x80x9d arm. Both arms have an anchored end and a free end. Each anchored end is fixed to a substrate and the free ends of the two arms are connected together by a thin member. The hot arm is a relatively thin member and the cold arm is a relatively thick member. Both arms have a thin flexure near the anchored end. The actuator is triggered by applying an electric current through the actuator, from anchor to anchor. The thin, hot arm has a higher current density than the thick, cold arm, due to its comparatively smaller cross-sectional area. The high current density causes the hot arm to heat and expand more than the cold arm. Because the arms are connected at the free end, the differences in expansion causes the actuator to bend such that the free end moves along an arc. This actuator functions in a manner similar to a bimetallic strip, in which the different expansion properties of the two metals cause the strip to curl. Multiple xe2x80x9cUxe2x80x9d shaped actuators may be connected to a common actuating structure form an array that compounds their output forces. This is accomplished by attaching a flexible yoke between the free end of the actuator and the common actuating structure. This flexible yoke is required to translate the arc-like motion into a linear actuation.
While this configuration does provide functional force and displacement characteristics, the xe2x80x9cUxe2x80x9d shaped actuator possesses multiple deficiencies. For example, arc incurred losses during conversion of the arcing output motion into linear translating motion. More specifically, the actuators in the array must expend a portion of their output energy to deform the flexible yokes so that the common actuating structure moves in a straight line. Additionally, the cold arm""s bulky size resists deflection as the hot arm arcs towards the cold arm. The force required to bend the cold arm does not contribute to the ultimate output force at he xe2x80x9cUxe2x80x9d shaped microactuator. Furthermore, the cold arm requires material, volume, and energy but does not contribute to the actuating force. The noncontributing material, volume, and energy become even more burdensome when multiple xe2x80x9cAxe2x80x9d shaped actuators are connected to form an array. The flexible yoke members similarly require energy, material, and volume without contributing to the output force produced by the actuator. Thus, the bulk and energy requirements fo the xe2x80x9cUxe2x80x9d shaped actuator make such actuators unsuitable for certain applications.
Accordingly, a need exists for a microactuator that can provide a high output force and high displacements, while operating at a low input voltage. Furthermore, the actuator should be lightweight and small, and should continue to operate in the presence of contaminants common in microcircuit applications. The microactuator should have a flexible design that can be easily adapted to suit various input, output, size, and material specifications. Moreover, the microactuator should be simple and easy to manufacture, preferably through methods similar to those used to make the circuits in which they operate.
The present micromechanism includes a microactuator that has advantageous size, displacement, and force characteristics. The micromechanism may comprise a generally long and thin expansion member that is coupled at a first end to a base member and at a second end to a displaceable shuttle. In one embodiment, the expansion member extends towards and the shuttle at an angle slightly offset from a perpendicular attachment to the base member. The expansion member may be configured to elongate in an elongation direction. The shuttle may be configured to travel in an output direction along a single axis. The displaceable shuttle may be constrained such that the lateral distance between the base member and the axis of shuttle""s output direction is fixed. This output direction is substantially different from the elongation direction of the expansion member. In one embodiment, the shuttle travels in a direction nearly perpendicular to the elongation direction of the expansion member. The expansion member is comprised of a material that can be formed microscopically. The material and shape of the expansion member may be selected such that substantial elongation occurs when thermal energy increases in the expansion member.
Upon an increase of thermal energy within the expansion member, the expansion member elongates in a direction nearly perpendicular to the base member and shuttle. Since the lateral offset of the base member and shuttle is constant, the expansion member cannot expand perpendicular to the shuttle. The expansion member""s movement at the base member coupling is limited to slight angular rotation and movement at the shuttle coupling is limited to the uniaxial travel of the shuttle. These limitations may force the expansion member to pivot near the base member end and drive the shuttle at the shuttle end. Relative motion between the base member and the shuttle permits pivoting of the expansion member such that the increased length of the expansion member can be accommodated. The result is that a relatively small elongation of the expansion member creates a large displacement of the shuttle.
The microactuators disclosed herein may function substantially in-plane, which entails operation of each component within a single plane. Thus, the microactuator may be made through film deposition methods similar to those used to construct flat circuits. In fact, a microactuator according to the invention may even be made simultaneously and unitarily with a circuit so that production can be econoznically and rapidly carried out. The low voltage requirement makes such microactuators operative for CMOS applications and the like, and their high force/displacement characteristics make them uniquely suited to other applications in which efficient motion is desirable. In addition, the simple design of the microactuators of the present invention enables them to continue operating even in the presence of small contaminants often found in circuit environments.
The purpose, function, and advantages of the present mechanism will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.